refactor(arcade): move config validation to game definitions

This implements Critical Fix #3 from AUDIT_2_ARCHITECTURE_QUALITY.md

Changes:
1. Add validateConfig to GameDefinition type
2. Update defineGame() to accept validateConfig function
3. Add validation functions to Number Guesser and Math Sprint
4. Update game-config-helpers.ts to use registry validation

Before (switch statement in helpers):
  - validateGameConfig() had 50+ line switch statement
  - Must update helper for every new game
  - Validation logic separated from game

After (validation in game definition):
  - Games own their validation logic
  - validateGameConfig() calls game.validateConfig()
  - Switch only for legacy games (matching, memory-quiz, complement-race)
  - New games: just add validateConfig to defineGame()

Example (Number Guesser):
  function validateNumberGuesserConfig(config: unknown): config is NumberGuesserConfig {
    return (
      typeof config === 'object' &&
      config !== null &&
      typeof config.minNumber === 'number' &&
      typeof config.maxNumber === 'number' &&
      typeof config.roundsToWin === 'number' &&
      config.minNumber >= 1 &&
      config.maxNumber > config.minNumber &&
      config.roundsToWin >= 1
    )
  }

Benefits:
✅ Eliminates switch statement boilerplate
✅ Single source of truth for validation
✅ Games are self-contained
✅ No helper updates needed for new games

To add a new game now:
1. Define validation function in game index.ts
2. Pass to defineGame({ validateConfig })
That's it! No helper file changes needed.

apps/web/src/arcade-games/math-sprint/index.ts

@@ -34,10 +34,28 @@ const defaultConfig: MathSprintConfig = {
   timePerQuestion: 30,
 }
 
+// Config validation function
+function validateMathSprintConfig(config: unknown): config is MathSprintConfig {
+  return (
+    typeof config === 'object' &&
+    config !== null &&
+    'difficulty' in config &&
+    'questionsPerRound' in config &&
+    'timePerQuestion' in config &&
+    ['easy', 'medium', 'hard'].includes((config as any).difficulty) &&
+    typeof (config as any).questionsPerRound === 'number' &&
+    typeof (config as any).timePerQuestion === 'number' &&
+    (config as any).questionsPerRound >= 5 &&
+    (config as any).questionsPerRound <= 20 &&
+    (config as any).timePerQuestion >= 10
+  )
+}
+
 export const mathSprintGame = defineGame<MathSprintConfig, MathSprintState, MathSprintMove>({
   manifest,
   Provider: MathSprintProvider,
   GameComponent,
   validator: mathSprintValidator,
   defaultConfig,
+  validateConfig: validateMathSprintConfig,
 })

apps/web/src/arcade-games/number-guesser/index.ts

@@ -34,6 +34,23 @@ const defaultConfig: NumberGuesserConfig = {
   roundsToWin: 3,
 }
 
+// Config validation function
+function validateNumberGuesserConfig(config: unknown): config is NumberGuesserConfig {
+  return (
+    typeof config === 'object' &&
+    config !== null &&
+    'minNumber' in config &&
+    'maxNumber' in config &&
+    'roundsToWin' in config &&
+    typeof config.minNumber === 'number' &&
+    typeof config.maxNumber === 'number' &&
+    typeof config.roundsToWin === 'number' &&
+    config.minNumber >= 1 &&
+    config.maxNumber > config.minNumber &&
+    config.roundsToWin >= 1
+  )
+}
+
 // Export game definition
 export const numberGuesserGame = defineGame<
   NumberGuesserConfig,
@@ -45,4 +62,5 @@ export const numberGuesserGame = defineGame<
   GameComponent,
   validator: numberGuesserValidator,
   defaultConfig,
+  validateConfig: validateNumberGuesserConfig,
 })

apps/web/src/lib/arcade/game-config-helpers.ts

@@ -17,6 +17,7 @@ import {
   DEFAULT_NUMBER_GUESSER_CONFIG,
   DEFAULT_MATH_SPRINT_CONFIG,
 } from './game-configs'
+import { getGame } from './game-registry'
 
 /**
  * Extended game name type that includes both registered validators and legacy games
@@ -176,8 +177,20 @@ export async function deleteAllGameConfigs(roomId: string): Promise<void> {
 /**
  * Validate a game config at runtime
  * Returns true if the config is valid for the given game
+ *
+ * NEW: Uses game registry validation functions instead of switch statements.
+ * Games now own their own validation logic!
  */
 export function validateGameConfig(gameName: ExtendedGameName, config: any): boolean {
+  // Try to get game from registry
+  const game = getGame(gameName)
+
+  // If game has a validateConfig function, use it
+  if (game?.validateConfig) {
+    return game.validateConfig(config)
+  }
+
+  // Fallback for legacy games without registry (e.g., complement-race, matching, memory-quiz)
   switch (gameName) {
     case 'matching':
       return (
@@ -206,31 +219,8 @@ export function validateGameConfig(gameName: ExtendedGameName, config: any): boo
       // TODO: Add validation when complement-race settings are defined
       return typeof config === 'object' && config !== null
 
-    case 'number-guesser':
-      return (
-        typeof config === 'object' &&
-        config !== null &&
-        typeof config.minNumber === 'number' &&
-        typeof config.maxNumber === 'number' &&
-        typeof config.roundsToWin === 'number' &&
-        config.minNumber >= 1 &&
-        config.maxNumber > config.minNumber &&
-        config.roundsToWin >= 1
-      )
-
-    case 'math-sprint':
-      return (
-        typeof config === 'object' &&
-        config !== null &&
-        ['easy', 'medium', 'hard'].includes(config.difficulty) &&
-        typeof config.questionsPerRound === 'number' &&
-        typeof config.timePerQuestion === 'number' &&
-        config.questionsPerRound >= 5 &&
-        config.questionsPerRound <= 20 &&
-        config.timePerQuestion >= 10
-      )
-
     default:
-      return false
+      // If no validator found, accept any object
+      return typeof config === 'object' && config !== null
   }
 }

apps/web/src/lib/arcade/game-sdk/define-game.ts

@@ -36,6 +36,9 @@ export interface DefineGameOptions<
 
   /** Default configuration for the game */
   defaultConfig: TConfig
+
+  /** Optional: Runtime config validation function */
+  validateConfig?: (config: unknown) => config is TConfig
 }
 
 /**
@@ -63,7 +66,7 @@ export function defineGame<
   TState extends GameState,
   TMove extends GameMove,
 >(options: DefineGameOptions<TConfig, TState, TMove>): GameDefinition<TConfig, TState, TMove> {
-  const { manifest, Provider, GameComponent, validator, defaultConfig } = options
+  const { manifest, Provider, GameComponent, validator, defaultConfig, validateConfig } = options
 
   // Validate that manifest.name matches the game identifier
   if (!manifest.name) {
@@ -76,5 +79,6 @@ export function defineGame<
     GameComponent,
     validator,
     defaultConfig,
+    validateConfig,
   }
 }

apps/web/src/lib/arcade/game-sdk/types.ts

@@ -77,4 +77,13 @@ export interface GameDefinition<
 
   /** Default configuration */
   defaultConfig: TConfig
+
+  /**
+   * Validate a config object at runtime
+   * Returns true if config is valid for this game
+   *
+   * @param config - Configuration object to validate
+   * @returns true if valid, false otherwise
+   */
+  validateConfig?: (config: unknown) => config is TConfig
 }